In recent years, specifying what a person pays attention to or thinks by measuring the direction of the person's gaze, has gained popularity in many fields. Techniques of non-contact detection of the direction of a person's gaze have been proposed in the past (see, for example, Patent Document 1 and Patent Document 2).
The gaze recognition apparatus disclosed in Patent Document 1 photographs an image of a person who is the target of gaze direction detection (hereinafter “subject”) using a stereo camera, analyzes the photographed image and detects the three dimensional positions of the center of the pupil, the inner corner and the outer corner of one eye. Next, presuming that the inner and outer corners of the eye are located on the spherical exterior of the eyeball, the gaze recognition apparatus specifies the three dimensional position of the center of the subject's eyeball based on the position of the inner corner of the eye, the position of the outer corner of the eye and the radius of the eyeball. Further, the gaze recognition apparatus calculates a vector starting from the center of the eyeball and ending at the center of the pupil, as a vector to indicate the direction of the subject's gaze.
Further, the gaze direction detecting apparatus disclosed in Patent Document 2 analyzes an image of the subject photographed by a stereo cameras and calculates the three dimensional positions of the center of the subject's pupil and the plane where the contour of the subject's pupil passes. Further, the gaze direction detecting apparatus detects the direction where the normal passes the center of the pupil amongst the normals passing the plane where the contour of the pupil passes, as the direction of the subject's gaze.    Patent Document 1: Japanese Patent Application Laid-open No. 2003-15816    Patent Document 2: Japanese Patent Application Laid-open No. 2004-255074